A broadband wireless access system is a system that defines a terminal MS, a base station BS, and a router ACR so as to be compatible with an existing public IP network, and provides a technique that makes a terminal have mobility, thereby allowing an IP-based network service to be used while the terminal is moved. An existing broadband wireless access system provides a structure where one terminal can communicate with a base station through only a band belonging to one FA.
Meanwhile, as a developed existing broadband wireless access system, there has been developed a broadband wireless access system where one terminal can communicate with a base station through a plurality of FAs. Herein, a function for the terminal to communicate with the base station by using a plurality of FAs is referred to as a frequency overlay function. According to the developed broadband wireless access system (hereinafter referred to as a “frequency overlay communication system”), the structure where a base station is connected to a public IP network is the same as an existing broadband wireless access system (hereinafter referred to as a “non-frequency overlay communication system”), and a wireless access portion between the base station and the terminal is different from a non-frequency overlay communication system. That is, the difference is as follows: the base station and the terminal communicate with each other through a plurality of frequency bandwidths that have access by using two or more FAs. Merits of the frequency overlay communication system having the above-mentioned characteristics are as follows: the frequency overlay communication system can use a band N times as large as a band of a non-frequency overlay communication system by slightly changing a wireless access method between a terminal and a base station, and a function of a MAC layer related thereto, e.g., it is possible to use a band twice as large under the assumption that one terminal uses two FAs. In conclusion, an available band is increased in proportion to the number of FAs used by the terminal. For this reason, it is possible to increase transmission speed between the terminal and the base station by two times or more (in general, when the number of FAs used between the terminal and the base station is N, transmission speed is increased by N times as compared to a non-frequency overlay communication system that uses one FA).
In this frequency overlay communication system, a large load is generated in a specific FA used by the base station while a base station and a terminal communicate with each other by using a plurality of FAs. For this reason, the use efficiency of the base station may considerably deteriorate. The base station communicates with the terminal by using a plurality of FAs. However, substantially, most of various control signals are transmitted through one FA (a primary FA, hereinafter referred to as a “pFA”) specified from the plurality of FAs, and data traffic is also transmitted. Therefore, when one FA of the plurality of FAs used by the base station communicates with a plurality of terminals and operates as a plurality of pFAs, a case where a load is concentrated on the FA occurs.
When pFAs of a plurality of FAs used for communication between the base station and the terminal are set in a frequency overlay communication system in the related art, the pFAs cannot be changed until the communication is completed. Therefore, the above-mentioned problem occurs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.